1. Field of the Invention
The present disclosure relates to a loop filter, and more particularly, to a loop filter for a continuous-time delta sigma modulator (DSM.)
2. Description of Related Art
A continuous-time delta signal modulator is a data converter which is widely used for realization of high efficiency in a wireless communication system such as a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and a Worldwide Interoperability for Microwave Access (WiMax), according to its anti-aliasing characteristics and high signal-to-noise ratio (SNR). Currently, advancement of manufacturing technologies and increased interests on low-power consumption cause much effort to design low-power delta sigma modulators.
Among blocks constituting a delta sigma modulator, a loop filter is a block which consumes the most power. Therefore, it's required to reduce power consumption and size of the loop filter by designing an enhanced structure of the loop filter. With respect to the design of the loop filter, various structures for the loop filter, which can reduce power consumption and size of the loop filter by configuring a second-order loop filter with a single operational (OP) amplifier, have been introduced. For reference, Korean patent publication No. 10-2015-0094906 disclosed a method for configuring a second-order loop filter using a single OP amplifier.
However, there are not examples in which a third-order loop filter is implemented using a single OP amplifier. It is not easy to find out a circuit configuration satisfying a third-order transfer function by using connections of resistors and capacitors when the order of the loop filter is 3 or above. Also, it is very difficult to provide a loop filter stable for changes in capacitances and resistances due to manufacturing tolerances.